The objectives of this research are to determine: 1) the cellular requirements for activation of antibody producing B cells and whether these requirements may differ for T "independent" and T "dependent" antigens by a) determining whether the ability of Type III Pneumococcal Polysaccharide (S3) to elicit IgG memory responses is T cell dependent and b) whether S3-specific "helper" T cells may play a role in immune responses to S3; 2) the role of "suppressor" T cells in the regulation of immune responses to S3 and in the regulation of autoimmune disease by a) determining the cell type affected by suppressor T cells, b) by determining whether S3 may normally activate "suppressor" rather than "helper" T cells and c) determining whether suppressor cells are lost in New Zealand mice as they age; and, 3) the nature of the cellular defect in mice which are genetic low responders to S3 by determining a) the relative roles of "suppressor" and "helper" T cells in the S3 response of high and low responder mice, and b) by determining whether low responders might have a B cell or macrophage defect. Antibody responses to S3 will be determined by the Jerne plaque assay and by hemagglutination. Effects of T cells on the S3 response will be determined directly, i.e. by transferring column purified T cells with B cells in adoptive transfer experiments and indirectly, by measuring effects of antilymphocyte serum, allogeneic T cells, etc. on immune responses to S3.